Magnetic recording and playing of a magnetic signal in a flexible magnetic disc comprising a disc sheet in a jacket, involving connecting a sheet-position determining part of a writing and/or reading apparatus to a central circular hole of the jacket and sheet, and rotating the disc sheet (the term "sheet" is also used hereinafter to refer to the disc sheet), is known. For the sheet to be stored in the jacket, a space is provided in a jacket which is slightly larger than the sheet, and thus the sheet in some cases moves to an eccentric position in the jacket during use or storage, with the result that the central circular hole of the sheet deviates from the position of a position-determining part (collet) of the apparatus when disc is loaded on the apparatus, and the sheet may be supported at an eccentric position at the position determining time.
FIG. 1A and FIG. 1B illustrates this type of flexible magnetic sheet, located in a rectangular jacket 1 having a circular open part 1a, with circular flexible magnetic sheet 2 having central circular hole 2a thereof exposed in the afore-mentioned central circular open part 1a, the sheet being stored in the jacket to allow free rotation thereof.
Upon loading this flexible magnetic disc on the writing and/or reading apparatus, rotating part 3 of the position-determining part is fitted from the under part of the sheet 2, and collet 4 is lowered toward the upper part of the sheet and is brought into the circular concave part 3a of rotating part 3 as shown in FIG. 2. A problem that sometimes occurs at this time is that the edge of central circular hole 2a does not always correspond to the position of circular concave part 2a of rotating part 3, and is many times out of proper alignment. If collet 4 is lowered in this state, some part of the portion surrounding the edge of circular hole 2a of the sheet 2 may be pinched between collet 4 and concave part 3a of rotating part 3, such that the sheet rotates eccentrically. Writing and reading cannot be carried out properly unless magnetic disc sheet 2 rotates while being correctly centered corresponding to the central rotating axis. Therefore, such eccentric pinching should very desirably be prevented. Moreover, there exists another problem, viz., that rattling occurs during rotation due to the absence of planarity of the sheet 2 when it is supported and rotated under such an eccentric pinched state.
Upon connecting the sheet 2 by lowering the collet 4, it is necessary that the portion surrounding the edge of the central circular hole of the sheet possesses an appropriate hardness, and that the friction coefficient (.mu.) between the sheet 2 and collet 4 as well as between the sheet 2 and rotating part 3 is small, in order that the sheet 2 is loaded correctly as shown in FIG. 4, not as shown in FIG. 3.
For this purpose, a method for reducing the friction coefficient by forming a protecting layer containing a polyolefin material polymerizable with ultraviolet light and an ester of an aliphatic acid on a surface portion surrounding the edge of the central hole of a flexible magnetic sheet where a sheet-position-determining part contacts the sheet has been disclosed in U.S. Pat. No. 4,387,114.
However, simply by forming a protecting layer containing resin hardenable and polymerizable with ultraviolet light, the intended purpose cannot be fully satisfactorily attained. Particularly, when such flexible magnetic sheets are piled in such a state that protective layers are in contact at the time of manufacturing magnetic sheets, protective layers adhere each other and blocking occurs due to planarity of the surface of the sheet and the softness of the resin and the like.
Additionally, in some cases the above described protective layer tends to adhere to the rotary portion of the collet when the flexible magnetic sheet is loaded on a disc drive in a cramped state for a long term use under conditions of high temperature and high humidity.